Due to the increase in data traffic in the operator's traffic, combined with the availability of Wi-Fi interface in most smartphones, operators look toward Wi-Fi as a supplementary capacity for offered services. This, however, may require higher coordination between 3GPP (3rd Generation Partnership Project) world and Wi-Fi and thus, in order to analyze the scope and means of a possible cooperation, a Study Item (SI) ‘Multi-RAT Joint Coordination’ was formed in RAN3 (cf. RP-132086 and TR 37.870). Among others, the SI addresses the question if any information exchange between 3GPP RAN (LTE in particular) and Wi-Fi is needed and, if so, what would be the most appropriate method to transfer this information. In pursuit of this, possible issues related to cooperation between Wi-Fi and LTE are being collected.
One of the problems related to the 3GPP RAN-Wi-Fi interaction is the absence or limited control of RAN over movement of UEs to a wireless communication network, like a wireless local area network (WLAN). Because the UE can automatically choose to select the available WLAN access point (AP), the 3GPP RAN does not get to know if the UE is attempting WLAN access and thus, is not aware of this. This prevents the RAN from controlling UE's traffic movement.
There are two reasons why the RAN might need better control over UE's movement. First, since the Quality of Service (QoS) management in WLAN network is not as granular and well defined as 3GPP RAN, the RAN might want to retain some selected services within itself to offer robust and reliable service to the UE. The QoS in WLANs can be different from the levels defined for the RAN such that switching the traffic path can have a negative effect on the required QoS. Second, because the RAN is the actual revenue generator for companies, the RAN would only want the WLAN to act as a supplementary radio access technology (RAT) and not share traffic indiscriminately, particularly when the RAN has free capacity. This would be an even bigger concern if the RAN providing company does not have a WLAN network of its own, because uncontrolled traffic in WLAN would negatively impact the RAN business case.
Currently, 3GPP RAN providers are using proprietary mechanisms to detect such UE movement. But there are proposals in Release 13 to solve this problem by making changes at the UE side to report any such activity.